Re: OT - Pulling Single Phase from 3 Phase Service

Posted by Gerald J. on August 07, 2007 at 08:39:15 from (67.0.103.11):

In Reply to: Re: OT - Pulling Single Phase from 3 Phase Service posted by John T on August 07, 2007 at 05:43:53:

Typically such a control transformer comes with two 240 volt windings and two 120 volt windings so it can be wired for 240 or 480 on the high side and 120 or 240/120 on the low side. That makes it more versatile than having just one winding for each side though it makes it cost a few pennies more for the added lead wires and internal splices. It reduces the need for inventory by three part numbers. I'm sure a 480 to 240 without center tap exists too. So its important to be sure the low side can be run 120/240. Then its important to know that if you put all the 120 volt load on one side, it may fry the transformer unless you increase its capacity to handle that unbalanced load.

A line to line load will still unbalance the 480 currents, and so the motor terminal voltages and thus the motor currents which exagurate the unbalance and if too unbalanced, fry a winding of the motor.

Gerald J.

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